Current mode hysteresis control optimization method based on Buck converter

Abstract

The invention provides a transient algorithm optimization method for current mode hysteresis control based on a Buck converter, which improves the transient response effect of the Buck converter under hysteresis control while simplifying an inductive current sampling circuit and improving the overall efficiency of a system. Through the rapid detection of the output current and the inductive current, the rapid recovery of the output voltage is realized by using an improved transient control algorithm.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converter control, and in particular relates to a transient optimization method based on Buck converter current mode hysteresis control. Background Art

[0002] With the continuous development of power electronics technology, converter control technology has also been improved. Current mode hysteresis control technology has the characteristics of good steady-state characteristics, high control accuracy, and good anti-interference performance, and has been widely used in engineering.

[0003] In the traditional current mode hysteresis control method, the control algorithms used by the transient control algorithm and the steady-state control algorithm are the same. By setting the desired output voltage, sampling the output load current, using the digital control method to calculate the average inductor current, and specifying the position of the hysteresis control upper and lower limits, the Buck converter can be controlled. Based on the traditional current mode hysteresis control strategy, in the transient response of a sudden increase in load current, after the inductor current value reaches the set new hysteresis control upper limit, the switch tube will be turned off. Since the output capacitor is in a discharge state for a long time when the transient switch tube is turned on, the output voltage of the converter will decrease after reaching a new steady state; the same is true in the transient response of a sudden drop in load current. After entering a new steady state, the output voltage will rise. Summary of the invention

[0004] In view of the problem of post-transient output voltage changes in traditional current mode hysteresis control in the background technology, the present invention proposes a transient control optimization method for a Buck converter with current mode hysteresis control, which improves the transient response effect of the Buck converter under hysteresis control while simplifying the inductor current sampling circuit and improving the overall efficiency of the system; a simple RC network is connected in parallel at both ends of the inductor to achieve rapid detection of the inductor current, and an improved transient control algorithm is used to achieve rapid recovery of the output voltage.

[0005] To achieve the above purpose, Figure 1 The control structure block diagram is shown, and the technical solution of the present invention is as follows:

[0006] 1. Parameter measurement: Sampling the real-time data of the Buck converter, measuring the output voltage and output current parameters of the converter through the sampling resistor, and measuring the inductor current parameters by connecting an RC circuit in parallel at both ends of the inductor;

[0007] 2. Hysteresis control: In steady state, the hysteresis width is calculated using the measured parameters. When the load undergoes transient changes, the upper and lower limits of the hysteresis are calculated using an optimized algorithm.

[0008] The mechanism of the present invention is as follows: utilizing an inductor current detection scheme of connecting RC circuits in parallel on both sides of the inductor to realize delay-free detection of the inductor current; utilizing a Buck converter transient response optimization algorithm to realize a balance between capacitor charging and discharging, thereby realizing rapid recovery of the converter output voltage during the transient response process.

[0009] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0010] The present invention utilizes the characteristic that the capacitor voltage is equivalent to the inductor current in the RC circuit to realize rapid detection of the inductor circuit. Compared with the traditional sampling resistor method, the loss of the converter is reduced and the overall efficiency of the system is improved. The hysteresis control transient optimization algorithm is utilized to solve the problem of unbalanced charging and discharging of the output capacitor under transient conditions, and rapid recovery of the output voltage parameters of the Buck converter is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Asynchronous Buck converter block diagram

[0012] Figure 2 Converter digital current mode hysteresis control optimization structure block diagram

[0013] Figure 3 Comparison chart before and after transient algorithm optimization

[0014] Figure 4 Transient circuit equivalent diagram, i.e. reference calculation module control block diagram

[0015] Figure 5 Simulation diagram before transient algorithm optimization

[0016] Figure 6 Simulation diagram after transient algorithm optimization DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0018] The control method of the present invention is designed for a Buck converter using hysteresis control. The simplified circuit diagram of the Buck converter is as follows: Figure 1 As shown in Figure 2. Among them, the circuit topology is as follows: Figure 1(a), which includes an inductor (L), a capacitor (C), a switch tube (S) and a diode (D); wherein the drain of the switch tube (S) is connected to one end of the inductor, and the source of the switch tube (S) is connected to the negative electrode of the input power supply; the cathode of the diode (D) is connected to one end of the inductor and the drain of the switch tube (S), the anode of the diode (D) is connected to one end of the output capacitor (C), and the other end of the output capacitor (C) is connected to one end of the inductor; the output capacitor (C) and the load (R) are connected in parallel. Figure 1 (b) and Figure 1 (c) are the equivalent circuit diagrams of the switch MOSFET being turned on or off. When the switch MOSFET is turned on, the inductor current stores energy, and when the switch MOSFET is turned off, the energy stored in the inductor is transferred to the load.

[0019] A digital current mode hysteresis control optimization method for Buck converter, its structure block diagram is as follows Figure 2 As shown, the following steps are included:

[0020] Step 1. Determine whether the circuit is in a steady state or a transient state. If it is a transient state, execute step 2; if it is a steady state, execute step 3. When the load current suddenly changes, the system enters a transient state. When the inductor current is limited to a specified hysteresis current range, the system works in a steady state.

[0021] Step 2. When the load changes from light load (small current) to heavy load (large current), the inductor current waveform under transient control is as follows: Figure 3 As shown in b. The switch tube S enters the on state, and the inductor current is approximately regarded as a linear increase. When it increases to the set upper limit value I2+H1, the switch tube S is turned off, and the inductor current is approximately regarded as a linear decrease. When the inductor current decreases to the new load current I2, the transient ends.

[0022] The H1 set during the transient process is set based on the balance of inductor current charging and discharging, such as Figure 3 As shown in b, during the time period t1 to t2, the load current suddenly changes. Since the inductor current cannot change instantly with the load current, the capacitor discharges during the time period t1 to t2. Figure 4 a shows the equivalent circuit diagram of the time period t1 to t2; during the time period t2 to t3, the inductor current is greater than the load current I2, and the capacitor is charged. Figure 4 b shows the circuit equivalent diagram from t2 to t3. At t3, the inductor current touches the set transient upper limit I2+H1, and the switch tube is turned off. During the time period from t3 to t4, the inductor circuit begins to decrease, but the inductor current is still greater than the new load current I2, so the output capacitor is still charged during the time period from t3 to t4.

[0023] It can be seen that during the transient process, the output capacitor discharges during the time period t1 to t2, and charges during the time period t2 to t4. The transient upper limit value I2+H1 is set based on the charge and discharge balance of the output capacitor. The charge change formula is as follows:

[0024] ΔQ=ΔI·Δt (1)

[0025] To facilitate analysis and formula calculation, combined Figure 3 b, assuming Δt1=t2-t1, Δt2=t3-t2, Δt3=t4-t3, the discharge charge of Δt1 is ΔQ1, the charge of Δt2 is ΔQ2, and the charge of Δt3 is ΔQ3.

[0026] When the switch tube S is turned on, the voltage across the inductor is approximately V i -V o , according to the formula It can be seen that the slope of the inductor current when it rises is (V i -V o ) / L, thus obtaining the expression of Δt1:

[0027]

[0028] The discharge charge at Δt1 is ΔQ1, which is expressed as:

[0029]

[0030] During the Δt2 period, the inductor current continues to rise and the rising slope remains the same. Similarly, the expression of Δt2 is obtained:

[0031]

[0032] The discharge charge at Δt2 is ΔQ2, which is expressed as:

[0033]

[0034] During the Δt3 period, the Buck converter switch is turned off, the inductor current decreases, and the voltage across the inductor is approximately V o , the inductor current decrease slope is V o / L, thus obtaining the expression for Δt3:

[0035]

[0036] The discharge charge at Δt3 is ΔQ3, which is expressed as:

[0037]

[0038] Based on the relationship that the amount of charge and discharge in the transient response of the capacitor is equal, the equation can be obtained:

[0039]

[0040] Solving H1 is:

[0041]

[0042] After t4, the Buck converter enters a new steady state, the inductor current continues to decrease, and because the switch tube continues to be turned off, the voltage across the inductor remains unchanged, and the slope of the inductor current decreases remains unchanged. When it drops to the hysteresis lower limit I2-ΔI / 2 of the new steady state, the switch tube is turned on, and the inductor current increases. When it rises to the hysteresis upper limit I2+ΔI / 2 of the new steady state, the switch tube is turned off, the inductor current decreases, and then this process is repeated.

[0043] Step 3. In steady state, the inductor current of the Buck converter operates in a range with a width of ΔI and a load current as the center line. When the lower limit of the hysteresis band is touched, the switch tube is turned on and the inductor current increases; when the upper limit of the hysteresis band is touched, the switch tube is turned off and the inductor current decreases.

[0044] according to Figure 3 It can be seen that in the steady-state state, the change in the inductor current when the switch tube of the Buck converter is turned on is the hysteresis loop width ΔI, and the inductor current rise time t on It can be expressed as:

[0045]

[0046] From this we can derive the expression for the hysteresis width:

[0047]

[0048] By substituting the switching frequency selected by the hysteresis control into the above formula, the steady-state hysteresis width ΔII can be obtained.

[0049] In order to verify the rapidity of output voltage recovery under transient conditions, simulation experiments are used for verification. The simulation results are shown in Figure 5 , Figure 6 shown.

[0050] The simulation parameters are as follows: Input voltage V i =12V, output voltage V o =5V, inductance L=10uH, capacitance C=470uF, initial load current I1=1A, load current after mutation I2=6A, switching frequency f=125k.

[0051] In summary, the present invention proposes a transient algorithm optimization method based on current mode hysteresis control of Buck converter, which simplifies the inductor current sampling circuit and improves the overall efficiency of the system, while improving the transient response effect of the Buck converter under hysteresis control; a simple RC network is connected in parallel at both ends of the inductor to achieve rapid detection of the inductor current, and an improved transient control algorithm is used to achieve rapid recovery of the output voltage.

[0052] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features or steps, can be combined in any way.

Claims

1. A digital current mode hysteresis control optimization method for a Buck converter, the structure block diagram of which is shown in FIG2, comprises the following steps: Step 1. Determine whether the circuit is in a steady state or a transient state. If it is a transient state, execute step 2; if it is a steady state, execute step 3. When the load current suddenly changes, the system enters a transient state. When the inductor current is limited to a specified hysteresis current range, the system works in a steady state. Step 2. When the load changes from light load (small current) to heavy load (large current), the switch tube S enters the on state, and the inductor current is approximately regarded as increasing linearly. When it increases to the set upper limit value I2+H1, the switch tube S is turned off, and the inductor current is approximately regarded as decreasing linearly. When the inductor current decreases to the new load current I2, the transient ends. H1 is set during transient conditions based on the balance of inductor current charging and discharging. Solving H1 is: After t4, the Buck converter enters a new steady state, the inductor current continues to decrease, and because the switch tube continues to be turned off, the voltage across the inductor remains unchanged, and the slope of the inductor current decreases remains unchanged. When it drops to the hysteresis lower limit I2-ΔI / 2 of the new steady state, the switch tube is turned on, and the inductor current increases. When it rises to the hysteresis upper limit I2+ΔI / 2 of the new steady state, the switch tube is turned off, the inductor current decreases, and then this process is repeated. Step 3. In steady state, the inductor current of the Buck converter operates in a range with a width of ΔI and a load current as the center line. When the lower limit of the hysteresis band is touched, the switch tube is turned on and the inductor current increases; when the upper limit of the hysteresis band is touched, the switch tube is turned off and the inductor current decreases. The expression of hysteresis width is: By substituting the switching frequency selected by the hysteresis control into the above formula, the steady-state hysteresis width ΔI can be obtained.

2. The digital hysteresis control optimization method according to claim 1, characterized in that: The topological structure of the Buck converter includes: a capacitor, an inductor, a diode and a switch tube; the drain of the switch tube is connected to one end of the inductor, and the source of the switch tube is connected to the negative electrode of the input power supply; the cathode of the diode is connected to one end of the inductor and the drain of the switch tube, the anode of the diode is connected to one end of the output capacitor, and the other end of the output capacitor is connected to one end of the inductor; the output capacitor and the load are connected in parallel.

3. The digital hysteresis control optimization method according to claim 1, characterized in that: The Buck converter operates in a continuous conduction mode during steady state.

4. The digital hysteresis control optimization method according to claim 1, characterized in that: The optimized transient condition is a light to heavy load change.

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